Position detecting device and position indicator thereof

ABSTRACT

A position detecting device includes: a position indicator including a signal generator configured to generate an alternating-current signal, a plurality of electrodes, a switch circuit configured to supply the alternating-current signal to selected one(s) of the electrodes based on a predetermined electrode-selection pattern, and a pattern information transmitter configured to transmit pattern information indicating a set predetermined pattern. A tablet includes electrodes disposed in a flat surface manner, a signal position detector configured to obtain a coordinate position of the alternating-current signal transmitted from said selected one(s) of the electrodes on a tablet surface based on distribution of a signal level induced in each of the tablet electrodes by the alternating-current signal, a pattern information receiver, and a rotation angle calculator configured to calculate a rotation angle of the position indicator about a perpendicular direction to the tablet surface based on a plurality of coordinate positions obtained according to the received pattern information.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority under 35 U.S.C. 119(a) toJapanese Patent Application No. 2012-176102, filed Aug. 8, 2012, whichis incorporated by reference herein.

BACKGROUND

1. Technical Field

The present invention relates to position detecting devices and positionindicators thereof, and particularly to a position detecting devicecapable of detecting a tilt of a position indicator having a pen shape,and/or a rotation angle of the position indicator about an axis definedby the perpendicular direction to a tablet surface, and a positionindicator thereof.

2. Description of the Related Art

As this type of device, a position detecting device of theelectromagnetic induction system is disclosed in Patent Document 1(Japanese Patent Laid-open No. Hei 8-30374). According to an embodimentexample of Patent Document 1, two magnetic cores are juxtaposed at thetip portion of a position indicator having a pen shape, and a controlcoil wound around only one magnetic core and a transmission coil that isso wound as to bundle two magnetic cores are provided. Both ends of thecontrol coil are controlled to the on- or off-state by an electronicswitch. Based on this, the distribution of magnetic flux made by acurrent flowing in the transmission coil is controlled to calculate arotation angle of the position indicator about the pen axis (alignedwith the perpendicular direction to the tablet surface), which isobtained as two coordinate positions in the position detecting device(hereinafter referred to as a “tablet” in this specification).

In another embodiment example of Patent Document 1, three magnetic coresare juxtaposed at the tip portion of a position indicator having a penshape, and three control coils wound around the respective magneticcores and a transmission coil that is so wound as to bundle threemagnetic cores are provided. By controlling the respective control coilssimilarly, a tilt of the position indicator relative to the tablet iscalculated.

SUMMARY OF THE INVENTION

The pen-shaped position indicator of the above-described Patent Document1 has a problem that the pen is thick because two magnetic cores arejuxtaposed at the tip part. Attempting to thin the magnetic cores tosolve this problem causes the following problems.

As a first problem, the distance between the centers of two magneticcores is shortened and thus the distance between two coordinatesdetected by the tablet is also shortened. This lowers the resolution andaccuracy in calculation of a rotation angle. This is attributed also tothe switch to control the control coil. This analog switch is configuredby a semiconductor circuit and therefore it is difficult to sufficientlylower the resistance value when it is turned on. Accordingly, it isdifficult to sufficiently suppress magnetic flux passing through themagnetic core surrounded by the control coil. Therefore, two coordinatesdetected by the tablet are obtained as values closer to each other thanthe actual core positions.

A second problem in thinning the magnetic cores is that shock due to,e.g., dropping of the pen breaks the core more easily. That the usepurpose of this kind of device is shifting to portable tablets in recentyears is also one of the reasons why demands for slimmer pens areincreasing.

Another problem (third problem) of the position detecting devicedescribed in Patent Document 1 is that integration with (finger) touchdetection is difficult. In recent years, multi-touch input of theelectrostatic induction system has come to be widely used and demandsfor a tablet device allowing both multi-touch input (by a finger) andpen input are increasing. However, in contrast to a tablet of theelectrostatic induction system, which uses a sensor obtained byarranging electrodes along the X direction and the Y direction, thetablet of the electromagnetic induction system of Patent Document 1needs to have a sensor obtained by arranging loop coils and therefore itis difficult to provide the tablet sensor as a sensor compatible withboth multi-touch input and pen input.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

According to aspects of the invention, all of the above-described first,second, and third problems are solved. Specifically, according to afirst aspect, a thin position indicator is provided whose rotation angleand tilt relative to the tablet surface can be accurately obtained.

According to a second aspect, a tough (durable) position indicator isprovided that is not easily broken due to shock of, e.g., being droppedeven when it is made to have a thin profile.

According to a third aspect, a position detecting device is provided, inwhich a sensor part of a touch panel based on the electrostatic couplingsystem can be used also as a tablet part.

According to an exemplary embodiment, a position detecting device isprovided that uses electrostatic coupling between a tablet and aposition indicator. In the case of using electromagnetic induction as inthe invention described in Patent Document 1 described above, if thecoil of the position indicator is thinned, not only the accuracy ofdetection of coordinates and rotation angle is significantly lowered butalso a core material as the core of the coil is easily broken. Thepresent invention makes improvements for the position detecting deviceof the electrostatic coupling system, in which a coil does not need tobe used in the position indicator, and has the following configuration.

The position indicator includes a signal generator that generates analternating-current signal, a plurality of electrodes disposed at aposition indicating part (e.g., a pen tip part), a switch circuit thatsupplies the alternating-current signal to selected one(s) of theelectrodes based on a predetermined electrode-selection pattern, and apattern information transmitter that transmits, to the tablet, patterninformation indicating a set predetermined pattern when the pattern isswitched by the switch circuit.

The tablet includes a plurality of electrodes disposed in a flat surfacemanner and a signal position detector that obtains the coordinateposition of the alternating-current signal transmitted from saidselected one(s) of the electrodes on the tablet surface based ondistribution of the level of a signal induced in each of the tabletelectrodes disposed in the flat surface manner. The tablet furtherincludes a pattern information receiver that receives the patterninformation transmitted from the position indicator, and a rotationangle calculator that calculates a rotation angle of the positionindicator about the perpendicular direction to the tablet surface basedon a plurality of coordinate positions obtained according to thereceived pattern information.

Furthermore, as another mode of the present invention, the presentinvention has the following configuration in conjunction with theabove-described configuration.

In the position indicator, at least three electrodes are provided at theposition indicating part (e.g., the pen tip part) and at least threekinds of predetermined patterns are provided as electrode-selectionpatterns selectable by the switch circuit.

The tablet includes the plurality of electrodes disposed in a flatsurface manner and the signal position detector that obtains thecoordinate position of the alternating-current signal transmitted fromsaid selected one(s) of the electrodes on the tablet surface based ondistribution of the level of a signal induced in each of the pluralityof electrodes disposed in the flat surface manner by thealternating-current signal transmitted from the position indicator. Thetablet further includes the pattern information receiver that receivesthe pattern information transmitted from the position indicator, and atilt angle calculator that calculates a tilt angle of the positionindicator relative to the tablet surface based on at least threecoordinate positions and at least three signal intensities obtainedaccording to the at least three kinds of predetermined patternsindicated by the pattern information received by the pattern informationreceiver.

According to embodiments of the present invention, the plural electrodesare provided at the position indicating part (e.g., pen tip part) of theposition indicator and the driven electrode(s) is switched time-wiseserially. This allows for determining a rotation angle of the positionindicator about the perpendicular direction to the tablet surface aswell as a tilt of the position indicator relative to the tablet surface.

According to embodiments of the present invention, electrostaticcoupling with the tablet is used. Thus, the position indicator, whoserotation angle and tilt can be obtained, can be realized in a thinprofile.

According to embodiments of the present invention, a magnetic materialsuch as a ferrite core does not need to be used for the positionindicator. Therefore, even when the position indicator, whose rotationangle and tilt can be obtained, is formed into a thin shape, theposition indicator is not easily broken due to shock from, e.g., beingdropped.

According to embodiments of the present invention, a coordinate positionis obtained by electrostatic coupling with the tablet. Therefore, thetablet sensor can be used commonly as the sensor for a touch panel ofthe electrostatic system, while at the same time achieving a positionindicator whose rotation angle and tilt can be obtained.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a structural diagram of a position indicating part in aposition indicator of a first embodiment example of the presentinvention;

FIG. 2 is a sectional view of a core in the position indicator of thefirst embodiment example of the present invention;

FIG. 3 is a circuit configuration diagram of the position indicator ofthe first embodiment example of the present invention;

FIG. 4 is a diagram for explaining the operation of the positionindicator of the first embodiment example of the present invention;

FIG. 5 is a configuration diagram of a tablet;

FIG. 6 is a diagram for explaining X-axis whole surface scan operationin the tablet;

FIG. 7 is a diagram for explaining transition operation to partial scanin the tablet;

FIGS. 8A-8B are diagrams that together constitute a single diagram ofFIG. 8 for explaining partial scan operation in the tablet of the firstembodiment example of the present invention;

FIG. 9 is a diagram for explaining the principle of rotation anglemeasurement;

FIG. 10 is a structural diagram of a position indicating part in aposition indicator of a second embodiment example of the presentinvention;

FIG. 11 is a diagram showing the arrangement of electrodes in theposition indicator of the second embodiment example of the presentinvention;

FIG. 12 is a circuit configuration diagram of the position indicator ofthe second embodiment example of the present invention;

FIG. 13 is a diagram for explaining the operation of the positionindicator of the second embodiment example of the present invention;

FIGS. 14A-14B are diagrams that together constitute a single diagram ofFIG. 14 for explaining partial scan operation in a tablet of the secondembodiment example of the present invention;

FIG. 15 is a structural diagram of a position indicating part in aposition indicator of a third embodiment example of the presentinvention;

FIG. 16 is a diagram showing the arrangement of electrodes in theposition indicator of the third embodiment example of the presentinvention;

FIG. 17 is a circuit configuration diagram of the position indicator ofthe third embodiment example of the present invention;

FIG. 18 is a diagram for explaining the operation of the positionindicator of the third embodiment example of the present invention;

FIGS. 19A-19B are diagrams that together constitute a single diagram ofFIG. 19 for explaining partial scan operation in a tablet of the thirdembodiment example of the present invention;

FIG. 20 is a diagram for explaining the principle of measurement of atilt of the position indicator of the third embodiment example of thepresent invention; and

FIG. 21 is a diagram for explaining examples of other shapes of the tippart of the position indicator.

DETAILED DESCRIPTION

Three embodiment examples will be specifically described below asposition detecting devices and position indicators thereof according toembodiments of this invention with reference to the drawings.

First Embodiment Example

FIG. 1 is a diagram showing the structure of a position indicating partin a position indicator of a first embodiment example according to thepresent invention. In FIG. 1, numeral 11 denotes a core that transmitspressure applied to the pen tip and it is molded by an insulatingmaterial such as plastic. Numeral 12 denotes a variable-capacitancecapacitor whose capacitance changes depending on the writing pressureapplied via the core 11 and, e.g., such as the one disclosed in JapanesePatent Laid-open No. Hei 4-96212 (Patent Document 2). Thevariable-capacitance capacitor 12 has a coupling part to the core 11 asdisclosed in the above-described Patent Document 2 and this couplingpart is so configured as to slightly move together with the core 11depending on the writing pressure applied to the core 11.

Numerals 13 and 14 denote electrodes and they are buried in the core 11.FIG. 2 is a sectional view when the core 11, in which the electrodes 13and 14 are buried, is cut. Numeral 15 denotes a printed board. Aterminal of the variable-capacitance capacitor 12 and the electrodes 13and 14 are connected to the printed board 15 and circuit components tobe described later are mounted on the printed board 15. In the followingdescription, the electrode 13 will be referred to as the L electrode andthe electrode 14 will be referred to as the R electrode.

FIG. 3 is a circuit configuration diagram of the position indicator ofthe first embodiment example according to the present invention. In FIG.3, the same component as that in FIG. 1 is shown by the same numeral.That is, numeral 12 denotes the variable-capacitance capacitor andnumerals 13 and 14 denote the L electrode and the R electrode,respectively. Transistors TR1 to TR3 configure an oscillation circuitthat oscillates with a resonant frequency depending on a coil L1 andcapacitors C1 and C2. A coil L2 is coupled to the coil L1 and boosts anAC voltage generated in the coil L1 to supply a signal of a high voltageto the L electrode 13 and the R electrode 14. Numeral 16 denotes ananalog switch for supplying a signal (d) generated in the coil L2 toonly either one of the L electrode 13 and the R electrode 14.

Numeral 17 denotes a microprocessor that operates based on apredetermined program and numeral 18 denotes a battery. An output signal(b) from a terminal P1 of the microprocessor 17 controls theabove-described oscillation circuit to the on- or off-state via atransistor TR4. An output signal (a) from a terminal P2 is supplied tothe analog switch 16. In the present embodiment example, the L electrode13 is selected when the output signal (a) from the terminal P2 is at thelow level and the R electrode 14 is selected when it is at the highlevel.

As described later, the microprocessor 17 sets a terminal P3 to the highlevel output state or the input state based on the predetermined programto thereby charge/discharge the variable-capacitance capacitor 12 andobtain the value of the writing pressure applied to the core 11.

Numeral 19 denotes a DC/DC converter that boosts the voltage of thebattery 18 to generate a power source of a high voltage VP. The voltageVP is used as a power source to make the analog switch 16 operate andneeds to be a voltage with amplitude higher than that of the signal dgenerated in the coil L2. A capacitor C3 is to add an offset voltage sothat the signal (d) generated in the coil L2 may swing in the range ofzero to VP.

FIG. 4 is a diagram showing the operation of the position indicator ofthe first embodiment example configured in this manner and shows how thesignals a, b, c, and d in FIG. 3 change. The microprocessor 17 carriesout control to keep the terminal P1 (signal b) at the high level for acertain period with the terminal P2 (signal a) set to the low level.Thereby, the signal (d) is radiated from the L electrode 13 for thecertain period continuously (continuous transmission period: L, in FIG.4). In this continuous transmission period, the microprocessor 17controls the terminal P3 to obtain the writing pressure applied to thevariable-capacitance capacitor 12. Specifically, the microprocessor 17sets the terminal P3 to the high level output state to charge thevariable-capacitance capacitor 12.

Next, the terminal P3 is switched to the input state. At this time, thecharge accumulated in the variable-capacitance capacitor 12 isdischarged by a resistor connected in parallel to it. Thus, the voltage(c) of the variable-capacitance capacitor 12 gradually decreases. A timeTp from the switch of the terminal P3 to the input state until thevoltage c is dropped to a threshold is obtained. This time Tp isequivalent to the writing pressure to be obtained and the writingpressure is obtained as a 10-bit value in the present embodimentexample.

Upon ending this continuous transmission period (L), the microprocessor17 controls the terminal P1 to the high or low level with apredetermined cycle (Td) to thereby perform amplitude-shift keying (ASK)modulation. At this time, the terminal P1 is invariably set to the highlevel as the first round of the control (start signal: L, in FIG. 4).This is to allow the tablet side to accurately determine the subsequentdata transmission timing.

In the period of Td following this start signal (L), the terminal P1 isset to the low level in this operation (sign: L, in FIG. 4). This is fordistinction from the case in which the terminal P2 (signal a) is set tothe high level as described later.

Subsequently to the sign (L), the 10-bit writing pressure data obtainedby the above-described operation is sequentially transmitted.Specifically, the terminal P1 is controlled to the low level when thetransmission data is 0 and the terminal P1 is controlled to the highlevel when the transmission data is 1 (writing pressure datatransmission period: L, in FIG. 4). FIG. 4 shows the case in which thewriting pressure to be transmitted is “0101110101.”

Upon ending the transmission of the 10-bit writing pressure data, themicroprocessor 17 sets the terminal P2 (signal a) to the high level toswitch the analog switch 16 to the R side. This provides the state inwhich a signal is transmitted from the R electrode 14. Also at thistime, the terminals P1 and P3 are controlled exactly as with theabove-described case of transmission by the L electrode to sequentiallyexecute processing of continuous transmission (R), start signal (R),sign (R), and writing pressure data transmission (R). At the time of thesign (R), the terminal P1 is set to the high level.

In the position indicator of the present embodiment example,transmission is performed with alternate switching between a firstpattern in which only the L electrode is selected and a second patternin which only the R electrode is selected. Furthermore, the “sign”information following the start signal is set to “0” when the selectionis made in the first pattern and the “sign” information following thestart signal is set to “1” when the selection is made in the secondpattern. Such operation is to identify, on the tablet side, whether theimmediately previous continuous transmission is from the L electrode orfrom the R electrode, and is one of features of the present invention.

FIG. 5 shows a configuration diagram of the tablet in the presentembodiment example. The present embodiment example shows, as the tablet,a configuration that obtains indicated position and rotation angle of aposition indicator 20 configured as described above and is capable alsoof detecting a touch position by a finger fg.

In FIG. 5, numeral 20 denotes the position indicator shown in FIGS. 1 to3 and the frequency of a signal transmitted from the position indicator20 is defined as f1. Numeral 21 denotes a tablet sensor whose basematerial is transparent glass. An X electrode group arranged in the Xdirection is provided on the front surface of the tablet sensor 21 and aY electrode group arranged in the Y direction is provided on the backsurface. These X electrode group and Y electrode group are formed astransparent electrodes by indium tin oxide (ITO). The tablet sensor 21is disposed on a display device (not shown) and an input can be madedirectly to its display place by the position indicator 20, the fingerfg of the user, etc.

Numeral 22 denotes an X selection circuit that selects one electrodefrom the X electrode group and numeral 23 denotes a Y selection circuitthat selects one electrode from the Y electrode group. The presentembodiment example will be explained based on the assumption that thenumber of X electrodes is 40 (X1 to X40) and the number of Y electrodesis 30 (Y1 to Y30).

Numeral 24 denotes an oscillator for supplying a drive signal to the Yelectrodes when the present embodiment example is operated for touchdetection and the oscillation frequency is defined as f2. Numeral 25denotes a switch circuit that switches the connection target of the Yelectrode selected by the Y selection circuit 23 to the oscillator 24 orthe side of an amplification circuit to be described later. Numeral 26denotes a control circuit to control the respective parts in the tabletof the present embodiment example. Specifically, when this device isoperated for touch detection, a control signal e from the controlcircuit 26 to the switch circuit 25 is set to the high level “1” toselect the side of the oscillator 24. When this device detects theposition indicator 20, the control signal e is set to the low level “0”to select the amplification circuit side.

Numeral 27 denotes a switch circuit. It selects the X electrode selectedby the X selection circuit 22 or selects the Y electrode selected by theY selection circuit 23 via the switch circuit 25 to connect it to anamplification circuit 28. Specifically, when this device is operated fortouch detection, a control signal f from the control circuit 26 to theswitch circuit 27 is set to the low level “0” to select the side of theX selection circuit 22. When this device is operated to detect theposition indicator 20 and the X-axis coordinate of the positionindicator 20 is to be obtained, the control signal f is set to the lowlevel “0” to select the side of the X selection circuit 22. When thisdevice is operated to detect the position indicator 20 and the Y-axiscoordinate of the position indicator 20 is to be obtained, the controlsignal f is set to the high level “1” to select the side of the Yselection circuit 23.

In FIG. 5, numeral 28 denotes the amplification circuit and numeral 29denotes a gain control circuit. The output of the amplification circuit28 is connected to the gain control circuit 29 and is so set as tobecome an output signal at a proper level by a control signal g from thecontrol circuit 26.

Numeral 30 denotes a band-pass filter circuit having a predeterminedband width centered at the frequency f1 or the frequency f2. This centerfrequency is switched by a control signal h from the control circuit 26.The frequency is switched to f1 when this device carries out operationof detecting the position indicator 20, and is switched to f2 when touchdetection operation is carried out.

In FIG. 5, numeral 31 denotes a detection circuit and numeral 32 denotesan analog/digital (AD) converter. Numeral 33 denotes a microprocessor.An output signal of the band-pass filter circuit 30 is detected by thedetection circuit 31 and is converted to a digital value by the ADconversion circuit 32 based on a control signal j from the controlcircuit 26. This digital data k is read and processed by themicroprocessor 33.

The control circuit 26 supplies a control signal m and a control signaln to the X selection circuit 22 and the Y selection circuit 23,respectively, to select one electrode from each of the X electrode groupand the Y electrode group.

The microprocessor 33 includes ROM and RAM inside and operates by aprogram stored in the ROM. The microprocessor 33 outputs a controlsignal p to control the control circuit 26 so that the control circuit26 may output the control signals e to j, m, and n at predeterminedtiming.

Operation when the tablet of the present embodiment example configuredin this manner performs touch detection will be briefly described. Asdescribed above, in the touch detection, the switch circuit 25 isconnected to the side of the oscillation circuit 24 to supply the drivesignal to the Y electrode selected by the Y selection circuit 23.Furthermore, the X electrode selected by the X selection circuit 22 isconnected to the amplification circuit 28 via the switch circuit 27 andthe signal level from the amplification circuit 28 is converted to adigital value by the AD conversion circuit 32 via the gain controlcircuit 29, the band-pass filter circuit 30, and the detection circuit31.

At this time, if a finger is made to touch the intersection of therespective electrodes selected by the X selection circuit 22 and the Yselection circuit 23, the detected signal level is lower than the levelwhen a finger is absent. Therefore, if the signal level when a finger isabsent is obtained in advance for all intersections of the X electrodesand the Y electrodes, the touch position can be obtained from theposition at which the signal level is lowered.

Operation when the tablet of the present embodiment example detectsindicated position and rotation angle of the position indicator 20 willbe described below. The microprocessor 33 outputs the control signal pto the control circuit 26 so that the control signal e may be set to thelow level “0” to select the amplification circuit side in the switchcircuit 25 and the control signal f may be set to the low level “0” toselect the X electrode side in the switch circuit 27. In this state,only the X electrode selected by the X selection circuit 22 is connectedto the amplification circuit 28 and the Y electrode is connected toneither the amplification circuit 28 nor the oscillation circuit 24.

FIG. 6 shows X-axis whole surface scan operation for obtaining the roughX-direction position of the position indicator 20 on the tablet sensor21. The microprocessor 33 makes the control circuit 26 output thecontrol signal m that causes the X selection circuit 22 to select theelectrode X1, and reads the signal level (k) at this time. Themicroprocessor 33 reads the signal level (k) while making the controlcircuit 26 sequentially switch the electrode selected by the X selectioncircuit 22 to the electrodes X2, X3, X4 . . . .

At this time, if the detected signal level does not reach apredetermined value with all electrodes X1 to X40, the microprocessor 33determines that the position indicator 20 is not present on the tabletsensor 21 and repeats the operation of FIG. 6. If a signal at a levelequal to or higher than the predetermined value is detected from any ofthe electrodes X1 to X40, the microprocessor 33 stores the number of theX electrode from which the highest signal level is detected (in FIG. 6,X11).

Upon getting to know that the position indicator 20 is present near theelectrode X11, the microprocessor 33 carries out transition operation topartial scan. FIG. 7 is a diagram for explaining the transitionoperation to the partial scan in the tablet. This transition operationto the partial scan is operation for the microprocessor 33 tosynchronize the timing with the operation of the position indicator 20by detecting the start time of the continuous transmission period of theposition indicator 20 when the position indicator 20 repeats operationlike that shown in FIG. 4, and to obtain the rough position about theY-axis.

In FIG. 7, the microprocessor 33 controls the control circuit 26 so thatthe X selection circuit 22 may select the electrode X11 obtained in theabove-described X-axis whole surface scan operation. At this time, asignal corresponding to the signal transmitted from the positionindicator 20 is induced in the electrode X11 and a voltage correspondingto its signal level is generated in the detection circuit 31. Themicroprocessor 33 makes the AD conversion circuit 32 operate with aconstant cycle to read the signal level (k). This cycle of the operationof the AD conversion circuit 32 is set to a time sufficiently shorterthan the cycle of transmission by the position indicator 20 in thewriting pressure data transmission period.

When the signal level output by the AD conversion circuit 32 is equal toor higher than a predetermined value for a certain time (Ts)continuously, the microprocessor 33 determines that the continuoustransmission period of the position indicator 20 has been started andtransitions to Y-axis whole surface scan operation (FIG. 7). This timeTs is set to a time sufficiently longer than the cycle of transmissionby the position indicator 20 in the writing pressure data transmissionperiod.

The microprocessor 33 controls the control circuit 26 so that thecontrol signal f may be set to the high level “1” to select the Yelectrode side in the switch circuit 27. Furthermore, the Y selectioncircuit 23 sequentially selects the electrodes from Y1 to Y30 and the ADconversion circuit 32 is operated to read the signal level (k). At thistime, the microprocessor 33 stores the electrode from which the highestsignal level is detected. The explanation of the present embodimentexample will be made based on the assumption that the highest signallevel is detected from the electrode Y20.

After the Y selection circuit 23 selects the last electrode Y30 anddetection of the signal level is ended, the microprocessor 33 carriesout operation for waiting for the end of the continuous transmissionperiod of the position indicator 20. The microprocessor 33 controls thecontrol circuit 26 so that the control signal f may be set to the lowlevel “0” to select the X electrode side in the switch circuit 27.Furthermore, the microprocessor 33 carries out control to make the Xselection circuit 22 select the electrode X11. At this time, a signal ata level equal to or higher than the above-described predetermined valueis detected if transmission from the position indicator 20 stillcontinues. The time at which the received signal level comes short ofthe predetermined value is the end time of the continuous transmissionfrom the position indicator 20. Subsequently, the position indicator 20enters the writing pressure data transmission period. However, thedetailed position of the position indicator 20 has not yet been obtainedat this timing. Thus, the microprocessor 33 does not read writingpressure data and transitions to partial scan operation shown in FIGS.8A-8B.

FIGS. 8A-8B are diagrams that together constitute a single diagram ofFIG. 8 for explaining the partial scan operation in the tablet of thepresent embodiment example. When the signal level output by the ADconversion circuit 32 is equal to or higher than the predetermined valuefor the certain time (Ts) continuously while the electrode X11 isselected, the microprocessor 33 determines that the continuoustransmission period of the position indicator 20 has been started andtransitions to coordinate detection operation (step 1 in FIG. 8A). Thistime Ts is the same as that explained with FIG. 7 and is set to a timesufficiently longer than the cycle of transmission by the positionindicator 20 in the writing pressure data transmission period.

In order to obtain the X coordinate of the signal from the positionindicator 20, the microprocessor 33 makes the X selection circuit 22sequentially select five electrodes centered at X11 (X9 to X13) with thecontrol signal f kept at the low level “0,” and makes the AD conversioncircuit 32 operate to read the signal level (step 1). At this time, thenumber of the electrode from which the highest signal level is detected(X11, in this example) and this signal level (Vpx0) are stored. Inaddition, the levels detected with both electrodes adjacent to thiselectrode are stored as Vax0 and Vbx0 (step 1).

Next, in order to obtain the Y coordinate of the signal from theposition indicator 20, the microprocessor 33 sets the control signal fto the high level “1.” Furthermore, the microprocessor 33 makes the Yselection circuit 23 sequentially select five electrodes centered at Y20(Y18 to Y22) and reads the signal level (step 1). At this time, thenumber of the electrode from which the highest signal level is detected(Y20, in this example) and this signal level (Vpy0) are stored. Inaddition, the levels detected with both electrodes adjacent to thiselectrode are stored as Vay0 and Vby0 (step 1). The obtained signallevels Vpx0, Vax0, Vbx0, Vpy0, Vay0, and Vby0 are used for calculationof coordinate values by a calculation equation to be described later.

Next, the microprocessor 33 carries out operation for waiting for theend of the continuous transmission period of the position indicator 20.The microprocessor 33 sets the control signal f to the low level “0” andcarries out control to make the X selection circuit 22 select theelectrode X11, from which the peak level is detected in theabove-described coordinate detection operation. At this time, the timeat which the received signal level comes short of the predeterminedvalue is the end time of the continuous transmission from the positionindicator 20 (step 1).

Upon detecting the end of the continuous transmission from the positionindicator 20, the microprocessor 33 enters operation of detecting thetiming of the start signal transmitted prior to writing pressure data(step 2). The microprocessor 33 carries out control to repeatedlyactivate the AD conversion circuit 32 with the electrode X11 selected,and stores the time at which the signal level becomes equal to or higherthan the above-described predetermined value as t1. The microprocessor33 starts operation of data reception from the position indicator 20from the time after waiting for a certain time Tw from the time t1 (step2). This time Tw is set to the time from the end of transmission of thestart signal from the position indicator 20 to the timing at which thesignal level received by the tablet becomes almost zero, and this timeis obtained in advance.

The microprocessor 33 activates a timer (not shown) simultaneously withthe timing at which the above-described waiting time reaches Tw. Thistimer repeatedly counts values from zero to the value corresponding withthe above-described time Td (cycle of data transmission from theposition indicator 20) (step 2). In the operation period of one cycle ofthe timer, the microprocessor 33 repeatedly activates the AD conversioncircuit 32 and reads the signal level. If the signal level during thisperiod never reaches the above-described predetermined value, themicroprocessor 33 determines that transmission from the positionindicator 20 is not made and stores the data of this round as “0.” If asignal level equal to or higher than the predetermined value is detectedin this period, the microprocessor 33 determines that transmission fromthe position indicator 20 is made and stores the data of this round as“1” (step 2).

The above-described timer count is performed eleven times and 11-bitdata is stored. In this data, the data of the first round is equivalentto the “sign” shown in FIG. 4. Because this sign is 0 in step 2 in FIG.8A, it turns out that the coordinates calculated from the signal levelsVpx0, Vax0, Vbx0, Vpy0, Vay0, and Vby0 obtained in step 1 are thecoordinate position corresponding to the L electrode of the positionindicator 20. The remaining 10-bit data represents the writing pressurevalue measured in the position indicator 20 in the period of step 1.

Although the electrode from which the maximum level is detected (X11) isselected from the X-axis electrodes and data is received in step 2, thisstep may be carried out by selecting the electrode from which themaximum level is detected (Y20) from the Y-axis electrodes.

Upon ending the reception of the 11-bit data in step 2, themicroprocessor 33 transitions to operation of detecting the start of thecontinuous transmission period of the position indicator 20. Themicroprocessor 33 repeatedly detects the signal level received with theelectrode X11 selected. When this reception level is equal to or higherthan the predetermined value for the certain time (Ts) continuously, themicroprocessor 33 determines that the continuous transmission period ofthe position indicator 20 has been started and transitions to coordinatedetection operation (step 3 in FIG. 8B).

In order to obtain the X coordinate of the signal from the positionindicator 20, the microprocessor 33 makes the X selection circuit 22sequentially select five electrodes centered at X11 (X9 to X13) with thecontrol signal f kept at the low level “0,” and makes the AD conversioncircuit 32 operate to read the signal level (step 3). At this time, thenumber of the electrode from which the highest signal level is detected(X11, in this example) and this signal level (Vpx1) are stored. Inaddition, the levels detected with both electrodes adjacent to thiselectrode are stored as Vax1 and Vbx1 (step 3).

Next, in order to obtain the Y coordinate of the signal from theposition indicator 20, the microprocessor 33 sets the control signal fto the high level “1.” Furthermore, the microprocessor 33 makes the Yselection circuit 23 sequentially select five electrodes centered at Y20(Y18 to Y22) and reads the signal level (step 3). At this time, thenumber of the electrode from which the highest signal level is detected(Y20, in this example) and this signal level (Vpy1) are stored. Inaddition, the levels detected with both electrodes adjacent to thiselectrode are stored as Vay1 and Vby1 (step 3). The obtained signallevels Vpx1, Vax1, Vbx1, Vpy1, Vay1, and Vby1 are used for calculationof coordinate values by a calculation equation to be described later.

Next, the microprocessor 33 carries out operation for waiting for theend of the continuous transmission period of the position indicator 20.The microprocessor 33 sets the control signal f to the low level “0” andcarries out control to make the X selection circuit 22 select theelectrode X11, from which the peak level is detected in theabove-described coordinate detection operation. At this time, the timeat which the received signal level comes short of the predeterminedvalue is the end time of the continuous transmission from the positionindicator 20 (step 3).

Upon detecting the end of the continuous transmission from the positionindicator 20, the microprocessor 33 enters operation of detecting thetiming of the start signal transmitted prior to writing pressure data(step 4). The microprocessor 33 carries out control to repeatedlyactivate the AD conversion circuit 32 with the electrode X11 selected,and stores the time at which the signal level becomes equal to or higherthan the above-described predetermined value as t2. The microprocessor33 starts operation of data reception from the position indicator 20from the time after waiting for the certain time Tw from the time t2(step 4). This Tw is set to the same time as that in step 2.

The microprocessor 33 activates the timer simultaneously with the timingat which the above-described waiting time reaches Tw and receives 11-bitdata from the position indicator 20 exactly as with the above-describedstep 2 (step 4). The data of the first round is equivalent to the “sign”shown in FIG. 4. Because this sign is 1 in step 4 in FIG. 8B, it turnsout that the coordinates calculated from the signal levels Vpx1, Vax1,Vbx1, Vpy1, Vay1, and Vby1 obtained in step 3 are the coordinateposition corresponding to the R electrode of the position indicator 20.The remaining 10-bit data represents the writing pressure value measuredin the position indicator 20 in the period of step 3. In this manner,identification as to which electrode of the position indicator 20 thetransmission is made from is allowed by the specific data value from theposition indicator 20. This is one of features of the present invention.

Although the electrode from which the maximum level is detected (X11) isselected from the X-axis electrodes and data is received also in step 4,this step may be carried out by selecting the electrode from which themaximum level is detected (Y20) from the Y-axis electrodes.

In the present embodiment example, the transmission from the positionindicator 20 by the L electrode and the transmission by the R electrodeare alternately repeated. Therefore, by repeatedly carrying out step 1to step 4 in FIG. 8B as the operation of the tablet side, thecoordinates, rotation angle, and writing pressure of the positionindicator 20 can be continuously obtained.

The method for obtaining the coordinate position and rotation angle ofthe position indicator 20 from the reception levels obtained in theabove-described step 1 and step 3 will be described below.

Coordinate values (X0, Y0) by the L electrode of the position indicator20 are calculated from the reception levels Vpx0, Vax0, Vbx0, Vpy0,Vay0, and Vby0 obtained in step 1 by the following equation (1) andequation (2), respectively.

$\begin{matrix}{{X\; 0} = {{P\; x\; 0} + {\frac{Dx}{2} \times \frac{{V\; {bx}\; 0} - {V\; {ax}\; 0}}{{2 \times V\; {px}\; 0} - {V\; {ax}\; 0} - {V\; {bx}\; 0}}}}} & (1)\end{matrix}$

In this equation, Px0 is the coordinate position of the electrode fromwhich the maximum level is detected regarding the X axis (X11, in thisexample) and Dx is the arrangement pitch between the X-axis electrodes.

$\begin{matrix}{{Y\; 0} = {{P\; y\; 0} + {\frac{y}{2} \times \frac{{V\; {by}\; 0} - {V\; {ay}\; 0}}{{2 \times V\; {py}\; 0} - {V\; {ay}\; 0} - {V\; {by}\; 0}}}}} & (2)\end{matrix}$

In this equation, Py0 is the coordinate position of the electrode fromwhich the maximum level is detected regarding the Y axis (Y20, in thisexample) and Dy is the arrangement pitch between the Y-axis electrodes.

Similarly, coordinate values (X1, Y1) by the R electrode of the positionindicator 20 are calculated from the reception levels Vpx1, Vax1, Vbx1,Vpy1, Vay1, and Vby1 obtained in step 3 by the following equation (3)and equation (4), respectively.

$\begin{matrix}{{X\; 1} = {{P\; x\; 1} + {\frac{Dx}{2} \times \frac{{V\; {bx}\; 1} - {V\; {ax}\; 1}}{{2 \times V\; {px}\; 1} - {V\; {ax}\; 1} - {V\; {bx}\; 1}}}}} & (3)\end{matrix}$

In this equation, Px1 is the coordinate position of the electrode fromwhich the maximum level is detected regarding the X axis (X11, in thisexample) and Dx is the arrangement pitch between the X-axis electrodes.

$\begin{matrix}{{Y\; 1} = {{{Py}\; 1} + {\frac{Dy}{2} \times \frac{{V\; {by}\; 1} - {V\; {ay}\; 1}}{{2 \times V\; {py}\; 1} - {V\; {ay}\; 1} - {V\; {by}\; 1}}}}} & (4)\end{matrix}$

In this equation, Py1 is the coordinate position of the electrode fromwhich the maximum level is detected regarding the Y axis (Y20, in thisexample) and Dy is the arrangement pitch between the Y-axis electrodes.

FIG. 9 is a principle diagram for calculating a rotation angle 8 of theposition indicator 20 about the axis defined as the perpendiculardirection to the tablet surface, based on two pairs of coordinate values(X0, Y0) and (X1, Y1). In this diagram, the orientation of the Relectrode corresponding to the coordinate values (X1, Y1) is defined byemploying the positive direction of the Y axis as the basis (θ=0) anddefining the range of θ as −180°<θ≦+180°. In this case, the rotationangle θ of the position indicator 20 is calculated from X0, Y0, X1, andY1 as shown by the following equations (5) to (9).

When Y1>Y0

$\begin{matrix}{\theta = {\tan^{- 1}( \frac{{X\; 1} - {X\; 0}}{{Y\; 1} - {Y\; 0}} )}} & (5)\end{matrix}$

When Y1=Y0 and X1>X0

θ=90°  (6)

When Y1=Y0 and X1<X0

θ=−90°  (7)

When Y1<Y0 and X1≧X0

$\begin{matrix}{\theta = {{180{^\circ}} + {\tan^{- 1}( \frac{{X\; 1} - {X\; 0}}{{Y\; 1} - {Y\; 0}} )}}} & (8)\end{matrix}$

When Y1<Y0 and X1<X0

$\begin{matrix}{\theta = {{{- 180}{^\circ}} + {\tan^{- 1}( \frac{{X\; 1} - {X\; 0}}{{Y\; 1} - {Y\; 0}} )}}} & (9)\end{matrix}$

In the present embodiment example, the Y-axis positive direction isdefined as the basis of the rotation angle and the orientation of the Relectrode (relative to the basis) is obtained as an angle. However, theX axis may be defined as the basis and the orientation of the Lelectrode may be obtained.

In the present embodiment example, the same information (writingpressure) is sent both in data transmission by the L electrode and indata transmission by the R electrode of the position indicator 20.However, another kind of information may be sent in one of them or onlysign information may be sent as one of the data to shorten the time.Furthermore, only one of the L electrode and the R electrode may be usedfor data transmission and the tablet may determine the electrode, withwhich the immediately previous continuous transmission is performed,based on whether data transmission from the position indicator 20 hasbeen made. Moreover, the frequency of transmission may be changedbetween transmission from the L electrode and transmission from the Relectrode to differentiate them or the length of the continuoustransmission may be changed for differentiation.

In the present embodiment example, the electrodes of the positionindicator 20 are exposed to the tip part of the core 11. However, theymay be covered by the material of the core 11, such as plastic.

Second Embodiment Example

FIG. 10 is a diagram showing the structure of a position indicating partin a position indicator of a second embodiment example according to thepresent invention. In FIG. 10, the same part as that in FIG. 1 is giventhe same reference numeral. That is, numeral 12 denotes avariable-capacitance capacitor whose capacitance changes depending onthe writing pressure and numeral 15 denotes a printed board. A core 35is coupled to the variable-capacitance capacitor 12 and the writingpressure applied to the tip of the core 35 is detected. Numeral 36denotes a chassis and a hole through which the core 35 passes is made atits tip part.

Two electrodes 37 and 38 are provided at the tip part of the chassis 36and FIG. 11 is a diagram showing the arrangement thereof. The followingdescription will be so made that the electrodes 37 and 38 are called theL electrode and the R electrode, respectively.

FIG. 12 is a circuit configuration diagram of the position indicator ofthe second embodiment example according to the present invention. InFIG. 12, the same part as that in FIG. 3 or FIG. 10 is given the samereference numeral. That is, numeral 12 denotes the variable-capacitancecapacitor. Numerals 37 and 38 denote the L electrode and the Relectrode, respectively. Numerals 17, 18, and 19 denote amicroprocessor, a battery, and a DC/DC converter, respectively.

The difference between the configuration of the position indicator ofthe second embodiment example shown in FIG. 12 and the configuration ofthe position indicator 20 of the first embodiment example shown in FIG.3 is as follows. In the first embodiment example, one of two electrodesis connected to the coil L2 with alternate switching. In contrast, inthe present embodiment example, the electrode 37 (L electrode) is alwaysconnected to the coil L2 and an analog switch 39 is provided between theelectrode 38 (R electrode) and the coil L2 and is controlled to the on-or off-state.

Specifically, when the terminal P2 (signal a) of the microprocessor 17is set to the high level, the analog switch 39 becomes the on-state andthus the signal (d) generated in the coil L2 is applied to both the Lelectrode and the R electrode. When the terminal P2 (signal a) of themicroprocessor 17 is set to the low level, the analog switch 39 becomesthe off-state and thus the signal (d) generated in the coil L2 isapplied to only the L electrode.

The voltage VP obtained by the DC/DC converter 19 is used as a powersupply to operate the analog switch 39 similarly to the first embodimentexample.

FIG. 13 is a diagram showing the operation of the position indicator ofthe second embodiment example and shows how the signals a, b, c, and din FIG. 12 change. The microprocessor 17 carries out control to keep theterminal P1 (signal b) at the high level for a certain period with theterminal P2 (signal a) set to the high level. Thereby, the signal (d) isradiated from the L electrode and the R electrode for the certain periodcontinuously (continuous transmission period: L+R, in FIG. 13). In thiscontinuous transmission period, the microprocessor 17 obtains thewriting pressure applied to the variable-capacitance capacitor 12similarly to the first embodiment example.

Upon ending this continuous transmission period, the microprocessor 17performs ASK modulation by controlling the terminal P1 with the cycle Tdexactly as with the first embodiment example. A sign (L+R) following thestart signal at this time is set to “0” indicating that the immediatelyprevious continuous transmission is made by two electrodes. Subsequentlyto this sign transmission, 10-bit writing pressure data obtained in theabove-described continuous transmission period is transmitted similarlyto the first embodiment example.

Upon ending the transmission of the writing pressure data, themicroprocessor 17 sets the terminal P2 (signal a) to the low level toturn off the analog switch 39. This provides the state in which a signalis transmitted from only the L electrode 37. Also at this time, theterminal P1 is similarly controlled to perform continuous transmission(L) and writing pressure detection is performed.

Upon ending this continuous transmission period, the microprocessor 17sets the terminal P2 (signal a) to the high level so that the subsequentdata transmission may be made by two electrodes. The purpose thereof isto allow the tablet to surely detect data of the writing pressure and soforth by transmitting the data by two electrodes. The microprocessor 17performs ASK modulation by controlling the terminal P1 with the cycle Tdsimilarly to the above description. A sign (L) following the startsignal at this time is set to “1” indicating that the immediatelyprevious continuous transmission is made by only the L electrode.Subsequently to this sign transmission, 10-bit writing pressure dataobtained in the above-described continuous transmission period issequentially transmitted.

In the position indicator of the present embodiment example,transmission is performed with alternate switching between a firstpattern in which both the L electrode and the R electrode are selectedand a second pattern in which only the L electrode is selected.Furthermore, the “sign” information following the start signal is set to“0” when the selection is made in the first pattern and the “sign”information following the start signal is set to “1” when the selectionis made in the second pattern. Such operation is to identify, on thetablet side, whether the immediately previous continuous transmission isfrom two electrodes or from only the L electrode, and is one of featuresof the present invention.

Also in the present embodiment example, the tablet having the sameconfiguration as that of the first embodiment example (FIG. 5) is used.Operation of detecting indicated position and rotation angle when theposition indicator of the present embodiment example is placed on thetablet of FIG. 5 will be described below.

Also in the present embodiment example, operation for obtaining therough position of the position indicator is carried out as shown inFIGS. 6 and 7 similarly to the first embodiment example. In FIG. 7, theY-axis whole surface scan operation after detection of continuoustransmission from the position indicator may be carried out in thecontinuous transmission period in which transmission from the positionindicator is made by two electrodes or may be carried out in thecontinuous transmission period in which transmission is made by only theL electrode. The explanation of the present embodiment example will alsobe made based on the assumption that the signal of the maximum level isdetected from the electrode X11 in the X-axis whole surface scanoperation in FIG. 6 and the signal of the maximum level is detected fromthe electrode Y20 in the Y-axis whole surface scan operation in FIG. 7.

FIGS. 14A-14B are diagrams that together constitute a single diagram ofFIG. 14, which shows partial scan operation of the second embodimentexample. The difference of the partial scan operation according to thepresent embodiment example from the partial scan operation of the firstembodiment example (FIGS. 8A-8B) is as follows. In the presentembodiment example, the coordinates obtained by coordinate detectionoperation (step 1 in FIG. 14A) immediately before the “sign” data fromthe position indicator is transmitted as “0” indicate the midpointposition between the L electrode and the R electrode (i.e., the positionof the core 35). Furthermore, the coordinates obtained by coordinatedetection operation (step 3 in FIG. 14B) immediately before the “sign”data from the position indicator is transmitted as “1” indicate theposition corresponding to the L electrode. The other operation is thesame as that in the first embodiment example.

Also in the present embodiment example, coordinate values indicating themidpoint position between the L electrode and the R electrode of theposition indicator are calculated as (X0, Y0) from the reception levelsVpx0, Vax0, Vbx0, Vpy0, Vay0, and Vby0 obtained in step 1 by using theabove-described equation (1) and equation (2).

Furthermore, coordinate values corresponding to the position of the Lelectrode of the position indicator are calculated as (X1, Y1) from thereception levels Vpx1, Vax1, Vbx1, Vpy1, Vay1, and Vby1 obtained in step3 by using the above-described equation (3) and equation (4).

The principle diagram of FIG. 9 is applied also to the presentembodiment example, so that the orientation of the L electrodecorresponding to the coordinate values (X1, Y1) is defined by employingthe positive direction of the Y axis as the basis (θ=0) and defining therange of θ as −180°<θ≦+180°. In this case, the rotation angle θ of theposition indicator is calculated by the above-described equations (5) to(9) with use of X0, Y0, X1, and Y1 in exactly the same way.

In the present embodiment example, the same information (writingpressure) is sent both in data transmission by two electrodes of theposition indicator and in data transmission by only the L electrode.However, another kind of information may be sent in one of them or onlysign information may be sent as one of the data to shorten the time.Furthermore, data transmission may be performed only at the time of thetransmission by two electrodes and the tablet may make the determinationdepending on whether data transmission from the position indicator hasbeen made. Alternatively, the length of the continuous transmission maybe changed to differentiate the transmission.

Although the electrodes of the position indicator are provided at thetip part of the chassis 36 in the present embodiment example, they maybe provided on the core 35 similarly to the first embodiment example.

Third Embodiment Example

FIG. 15 is a diagram showing the structure of a position indicating partin a position indicator of a third embodiment example according to thepresent invention. In the present embodiment example, an example isshown in which three electrodes are disposed in the position indicatorand a tilt of the position indicator relative to the tablet is obtainedin addition to a rotation angle thereof.

In FIG. 15, the same part as that in FIG. 10 is given the same referencenumeral. That is, numeral 12 denotes a variable-capacitance capacitorwhose capacitance changes depending on the writing pressure. Numerals15, 35, and 36 denote a printed board, a core, and a chassis,respectively.

Three electrodes 40, 41, and 42 are provided at the tip part of thechassis 36 and FIG. 16 is a diagram showing the arrangement thereof.These three electrodes are connected to the printed board 15 by aconnection line (not shown).

FIG. 17 is a circuit configuration diagram of the position indicator ofthe third embodiment example according to the present invention. In FIG.17, the same part as that in FIG. 15 or FIG. 3 is given the samereference numeral. That is, numeral 12 denotes the variable-capacitancecapacitor. Numerals 40 to 42 denote the electrodes. Numerals 17, 18, and19 denote a microprocessor, a battery, and a DC/DC converter,respectively.

The difference of the configuration shown in FIG. 17 from the firstembodiment example (FIG. 3) is as follows. In the first embodimentexample, one of two electrodes is connected to the coil L2 withalternate switching. In contrast, in the present embodiment example, oneof three electrodes 40 to 42 is connected to the coil L2 with sequentialswitching. An analog multiplexer 43 is provided between the electrodes40 to 42 and the coil L2 and one is selected among the electrode 40, theelectrode 41, and the electrode 42 by setting of two terminals of themicroprocessor 17 (P2 and P4). Signals from two terminals of themicroprocessor 17 (P2 and P4) are referred to collectively as the“signal a” here.

The voltage VP obtained by the DC/DC converter 19 is used as a powersupply to operate the analog multiplexer 43 similarly to the firstembodiment example.

FIG. 18 is a diagram showing the operation of the position indicator ofthe third embodiment example and shows how the signals a, b, c, and d inFIG. 17 change. The microprocessor 17 carries out control to keep theterminal P1 (signal b) at the high level for a certain period with theelectrode 40 selected by the setting by the signal a. Thereby, thesignal (d) is radiated from the electrode 40 for the certain periodcontinuously (continuous transmission period 1, in FIG. 18). In thiscontinuous transmission period, the microprocessor 17 obtains thewriting pressure applied to the variable-capacitance capacitor 12similarly to the first embodiment example.

Upon ending this continuous transmission period, the microprocessor 17performs ASK modulation by controlling the terminal P1 with the cycle Tdexactly as with the first embodiment example. The “sign” following the“start signal” at this time is set to “0” indicating that theimmediately previous continuous transmission is made by the electrode40. Subsequently to this sign transmission, 10-bit writing pressure dataobtained in the above-described continuous transmission period 1 istransmitted similarly to the first embodiment example.

Upon ending the transmission of the writing pressure data, themicroprocessor 17 switches the setting by the signal a to select theelectrode 41, and similarly controls the terminal P1 to performcontinuous transmission (continuous transmission period 2, in FIG. 18).At this time, writing pressure detection like that performed incontinuous transmission period 1 is not performed in the presentembodiment example.

Upon the end of this continuous transmission period 2, themicroprocessor 17 performs ASK modulation by controlling the terminal P1with the cycle Td while keeping of the selection of the electrode 41 bythe setting by the signal a. The “sign” following the start signal atthis time is transmitted as “1.”

Upon ending this sign transmission, the microprocessor 17 switches thesetting by the signal a to select the electrode 42, and similarlycontrols the terminal P1 to perform continuous transmission (continuoustransmission period 3, in FIG. 18). Also at this time, writing pressuredetection like that performed in continuous transmission period 1 is notperformed.

Upon the end of this continuous transmission period, the microprocessor17 performs ASK modulation by controlling the terminal P1 with the cycleTd while keeping of the selection of the electrode 42 by the setting bythe signal a. Also at this time, the “sign” following the start signalis transmitted as “1.”

In the position indicator of the present embodiment example, thefollowing patterns are set: a first pattern in which only the electrode40 is selected, a second pattern in which only the electrode 41 isselected, and a third pattern in which only the electrode 42 isselected. Transmission is performed with sequential repetition of thepatterns, i.e., like in the second pattern subsequently to the firstpattern, in the third pattern subsequently to the second pattern, and inthe first pattern subsequently to the third pattern. Furthermore, the“sign” information following the start signal is set to “0” when theselection is made in the first pattern and the “sign” informationfollowing the start signal is set to “1” when the selection is made inthe second pattern and the third pattern. Therefore, the tablet side canidentify which electrode of the position indicator a signal istransmitted from by considering the above-described transmission order.These operations are one of features of the present invention.

Also in the present embodiment example, the tablet having the sameconfiguration as that of the first embodiment example (FIG. 5) is used.Operation of detecting indicated position, rotation angle, and tiltrelative to the tablet surface when the position indicator of thepresent embodiment example is placed on the tablet of FIG. 5 will bedescribed below.

Also in the present embodiment example, operation for obtaining therough position of the position indicator is carried out as shown inFIGS. 6 and 7 similarly to the first embodiment example. In FIG. 7, anyelectrode may be used for transmission from the position indicator inthe continuous transmission period in which the Y-axis whole surfacescan operation after detection of continuous transmission from theposition indicator is carried out. The explanation of the presentembodiment example will also be made based on the assumption that thesignal of the maximum level is detected from the electrode X11 in theX-axis whole surface scan operation in FIG. 6 and the signal of themaximum level is detected from the electrode Y20 in the Y-axis wholesurface scan operation in FIG. 7.

FIGS. 19A-19B together constitute a single diagram of FIG. 19, whichshows partial scan operation of the third embodiment example. Also inthe present embodiment example, after a signal continuing for thecertain time (Ts) or longer from the position indicator is detected,coordinate detection operation of the X axis and the Y axis is carriedout. Then, data sent subsequently to continuous transmission from theposition indicator is received. This data is transmitted subsequently tothe “start signal” also as shown in FIG. 18. In the present embodimentexample, if “0” is received as the “sign” following immediately afterthe “start signal,” the data reception operation is continuously carriedout to receive 10-bit writing pressure data. If “1” is received as the“sign,” the data reception operation is ended and transition tooperation for detecting continuous transmission from the positionindicator is made.

In FIG. 19A, “0” is received as the sign in step 2. Thus, in theimmediately previous coordinate detection operation (step 1), the leveland coordinate position based on a signal transmitted from the electrode40 of the position indicator are obtained. In the subsequent coordinatedetection operation (step 3), the level and coordinate position based ona signal transmitted from the electrode 41 of the position indicator areobtained. In the further subsequent coordinate detection operation (step5), the level and coordinate position based on a signal transmitted fromthe electrode 42 of the position indicator are obtained.

In the present embodiment example, in order to obtain the tilt of theposition indicator by using the reception levels obtained in therespective coordinate detection operations of step 1, step 3, and step5, the gain value set in the gain control circuit 29 of the tabletcircuit (FIG. 5) is set identical in these respective coordinatedetection operations.

Coordinate values (X1, Y1) by the electrode 40 of the position indicatorare calculated from the reception levels Vpx1, Vax1, Vbx1, Vpy1, Vay1,and Vby1 obtained in step 1 by the above-described equation (3) andequation (4).

Furthermore, coordinate values (X2, Y2) by the electrode 41 of theposition indicator are obtained from reception levels Vpx2, Vax2, Vbx2,Vpy2, Vay2, and Vby2 obtained in step 3 by the following equation (10)and equation (11).

$\begin{matrix}{{X\; 2} = {{{Px}\; 2} + {\frac{D\; x}{2} \times \frac{{V\; {bx}\; 2} - {V\; {ax}\; 2}}{{2 \times V\; {px}\; 2} - {V\; {ax}\; 2} - {V\; {bx}\; 2}}}}} & (10)\end{matrix}$

In this equation, Px2 is the coordinate position of the electrode fromwhich the maximum level is detected regarding the X axis (X11, in thisexample) and Dx is the arrangement pitch between the X-axis electrodes.

$\begin{matrix}{{Y\; 2} = {{{Py}\; 2} + {\frac{Dy}{2} \times \frac{{V\; {by}\; 2} - {V\; {ay}\; 2}}{{2 \times V\; {py}\; 2} - {V\; {ay}\; 2} - {V\; {by}\; 2}}}}} & (11)\end{matrix}$

In this equation, Py2 is the coordinate position of the electrode fromwhich the maximum level is detected regarding the Y axis (Y20, in thisexample) and Dy is the arrangement pitch between the Y-axis electrodes.

Coordinate values (X3, Y3) by the electrode 42 of the position indicatorare obtained from reception levels Vpx3, Vax3, Vbx3, Vpy3, Vay3, andVby3 obtained in step 5 by the following equation (12) and equation(13).

$\begin{matrix}{{X\; 3} = {{{Px}\; 3} + {\frac{Dx}{2} \times \frac{{V\; {bx}\; 3} - {V\; {ax}\; 3}}{{2 \times V\; {px}\; 3} - {V\; {ax}\; 3} - {V\; {bx}\; 3}}}}} & (12)\end{matrix}$

In this equation, Px3 is the coordinate position of the electrode fromwhich the maximum level is detected regarding the X axis (X11, in thisexample) and Dx is the arrangement pitch between the X-axis electrodes.

$\begin{matrix}{{Y\; 3} = {{{Py}\; 3} + {\frac{Dy}{2} \times \frac{{V\; {by}\; 3} - {V\; {ay}\; 3}}{{2 \times V\; {py}\; 3} - {V\; {ay}\; 3} - {V\; {by}\; 3}}}}} & (13)\end{matrix}$

In this equation, Py3 is the coordinate position of the electrode fromwhich the maximum level is detected regarding the Y axis (Y20, in thisexample) and Dy is the arrangement pitch between the Y-axis electrodes.

Coordinate values (X0, Y0) corresponding to the core 35 of the positionindicator can be obtained as the center point of three obtainedcoordinate values (X1, Y1), (X2, Y2), and (X3, Y3) by the followingequation (14) and equation (15).

$\begin{matrix}{{X\; 0} = \frac{{X\; 1} + {X\; 2} + {X\; 3}}{3}} & (14) \\{{Y\; 0} = \frac{{Y\; 1} + {Y\; 2} + {Y\; 3}}{3}} & (15)\end{matrix}$

The principle diagram of FIG. 9 is applied also to the presentembodiment example, so that the orientation of the electrode 40corresponding to the coordinate values (X1, Y1) is defined by employingthe positive direction of the Y axis as the basis (θ=0) and defining therange of θ as −180°<θ≦+180°. In this case, the rotation angle θ of theposition indicator is calculated by the above-described equations (5) to(9) with use of X0, Y0, X1, and Y1 in exactly the same way.

In the present embodiment example, a tilt of the position indicator canbe obtained from the respective received signal intensities from threeelectrodes of the position indicator. As the received signal intensity,the level at the time of the X-axis coordinate detection may be used orthe level at the time of the Y-axis coordinate detection may be used.Here, the level at the time of the X-axis coordinate detection is used.

Received signal intensity (V1) by the electrode 40 is obtained bycorrection calculation by the following equation (16) based on the Xelectrode positions of the tablet.

$\begin{matrix}{{V\; 1} = {{V\; {px}\; 1} + \frac{( {{V\; {ax}\; 1} - {V\; {bx}\; 1}} )^{2}}{8 \times ( {{{2 \cdot V}\; {px}\; 1} - {V\; {ax}\; 1} - {V\; {bx}\; 1}} )}}} & (16)\end{matrix}$

Received signal intensity (V2) by the electrode 41 is obtained by thefollowing equation (17).

$\begin{matrix}{{V\; 2} = {{V\; {px}\; 2} + \frac{( {{V\; {ax}\; 2} - {V\; {bx}\; 2}} )^{2}}{8 \times ( {{{2 \cdot V}\; {px}\; 2} - {V\; {ax}\; 2} - {V\; {bx}\; 2}} )}}} & (17)\end{matrix}$

Received signal intensity (V3) by the electrode 42 is obtained by thefollowing equation (18).

$\begin{matrix}{{V\; 3} = {{V\; {px}\; 3} + \frac{( {{V\; {ax}\; 3} - {V\; {bx}\; 3}} )^{2}}{8 \times ( {{{2 \cdot V}\; {px}\; 3} - {V\; {ax}\; 3} - {V\; {bx}\; 3}} )}}} & (18)\end{matrix}$

FIG. 20 is a principle diagram for obtaining the tilt of the positionindicator by using the received signal intensities V1, V2, and V3 fromthree electrodes. In FIG. 20, the height direction from the sensorsurface (21 in FIG. 5) of the tablet is employed as the z axis and thecoordinate axes are so set that the center G of an equilateral triangleconfigured by A, B, and C corresponding to the tips of the electrodes40, 41, and 42, respectively, of the position indicator exists on the yzplane and point A corresponding to the tip of the electrode 40 exists onthe z axis. When the coordinates of the respective points at this timeare represented as point A (0, 0, z1), point B (x2, y2, z2), point C(x3, y3, z3), and point G (0, yg, zg), the tilt (θx, θy) of the positionindicator is obtained as shown by the following equation (19) andequation (20).

$\begin{matrix}{{\sin \; \theta \; x} = \frac{{z\; 2} - {z\; 3}}{r}} & (19)\end{matrix}$

(r: the length of one side of the equilateral triangle)

$\begin{matrix}{{\sin \; \theta \; y} = \frac{{{2 \cdot z}\; 1} - {z\; 2} - \; {z\; 3}}{r\sqrt{\;}3}} & (20)\end{matrix}$

(slope of the segment coupling point A and the midpoint between B and C)

The distances (z1, z2, z3) of point A, point B, and point C, which arethe tip positions of three electrodes of the position indicator, fromthe tablet sensor surface are almost inversely proportional to thereceived signal intensities V1, V2, and V3. Therefore, the relationshipsare represented as the following equation (21) and equation (22) withuse of α as a proportionality coefficient.

z1=α/V1, z2=α/V2, z3=α/V3 therefore, θx and θy are represented asfollows

$\begin{matrix}{{\theta \; x} = {\sin^{- 1}\frac{\alpha ( {{V\; 3} - {V\; 2}} )}{{r \cdot V}\; {2 \cdot V}\; 3}}} & (21) \\{{\theta \; y} = {\sin^{- 1}\frac{\alpha ( {{{2 \cdot V}\; {2 \cdot V}\; 3} - {V\; {1 \cdot V}\; 3} - {V\; {1 \cdot V}\; 2}} )}{{r \cdot V}\; {1 \cdot V}\; {2 \cdot V}\; {3 \cdot \sqrt{\;}}3}}} & (22)\end{matrix}$

Because α/r is a constant, obtaining this value in advance can obtain θxand θy from the above relationship equations.

Although three electrodes of the position indicator are provided at thetip part of the chassis 36 in the present embodiment example, they maybe provided on the core like in the first embodiment example.

In the present embodiment example, rotation angle and tilt of theposition indicator can be detected. Therefore, it is possible to shapethe tip part in an asymmetric (non-symmetric) shape like those shown inFIG. 21 for example; then, software may be used to generate (detect userinput of) drawings according to the obtained rotation angle and tilt.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. A position detecting device comprising: aposition indicator configured to transmit an alternating-current signal;and a tablet capable of being capacitively coupled to the positionindicator, wherein the position detecting device obtains a positionindicated by the position indicator on the tablet by capacitivelycoupling the position indicator and the tablet, the position indicatorincludes: a signal generator configured to generate analternating-current signal, a plurality of electrodes disposed at aposition indicating part of the position indicator, a switch circuitconfigured to supply the alternating-current signal to selected one(s)of the plurality of electrodes based on a predeterminedelectrode-selection pattern, and a pattern information transmitterconfigured to transmit, to the tablet, pattern information indicating aset predetermined pattern when the pattern is switched by the switchcircuit, and the tablet includes: a plurality of tablet electrodesdisposed in a flat surface manner, a signal position detector configuredto obtain a coordinate position of the alternating-current signaltransmitted from said selected one(s) of the electrodes on a tabletsurface based on distribution of a level of a signal induced in each ofthe tablet electrodes disposed in the flat surface manner by thealternating-current signal transmitted from the position indicator, apattern information receiver configured to receive the patterninformation transmitted from the position indicator, and a rotationangle calculator configured to calculate a rotation angle of theposition indicator about a perpendicular direction to the tablet surfacebased on a plurality of coordinate positions obtained according to thereceived pattern information.
 2. The position detecting device accordingto claim 1, wherein: in the position indicator, a first electrode and asecond electrode are disposed at the position indicating part as theplurality of electrodes, the switch circuit alternately selects thefirst and second electrodes and supplies the alternating-current signalto the selected one of the electrodes, and the pattern informationtransmitter transmits first pattern information to the tablet when thefirst electrode is selected by the switch circuit, and transmits secondpattern information to the tablet when the second electrode is selectedby the switch circuit; and in the tablet, a first coordinate is obtainedby the signal position detector when the first pattern information isreceived by the pattern information receiver, and a second coordinate isobtained by the signal position detector when the second patterninformation is received by the pattern information receiver, and therotation angle of the position indicator about the perpendiculardirection to the tablet surface is calculated based on the firstcoordinate and the second coordinate.
 3. The position detecting deviceaccording to claim 1, wherein: in the position indicator, a firstelectrode and a second electrode are disposed at the position indicatingpart as the plurality of electrodes, and the switch circuit alwayssupplies the alternating-current signal to the first electrode andswitches supply of the alternating-current signal to the secondelectrode between an on (supply)- and off (no supply)-state, and thepattern information transmitter transmits first pattern information tothe tablet when the supply of the alternating-current signal to thesecond electrode is set to the on-state by the switch circuit, andtransmits second pattern information to the tablet when the supply ofthe alternating-current signal to the second electrode is set to theoff-state by the switch circuit; and in the tablet, a coordinatecorresponding to a midpoint position of the first and second electrodesof the position indicator is obtained as a first coordinate by thesignal position detector when the first pattern information is receivedby the pattern information receiver, and a coordinate corresponding to aposition of the first electrode of the position indicator is obtained asa second coordinate by the signal position detector when the secondpattern information is received by the pattern information receiver, andthe rotation angle of the position indicator about the perpendiculardirection to the tablet surface is calculated based on the firstcoordinate and the second coordinate.
 4. A position detecting devicecomprising: a position indicator that transmits an alternating-currentsignal; and a tablet capable of being capacitively coupled to theposition indicator, wherein the position detecting device obtains aposition indicated by the position indicator on the tablet bycapacitively coupling the position indicator and the tablet, theposition indicator includes: a signal generator configured to generatean alternating-current signal, at least three electrodes disposed at aposition indicating part of the position indicator, a switch circuitconfigured to supply the alternating-current signal to selected one ofthe electrodes based on a predetermined electrode-selection pattern, anda pattern information transmitter configured to transmit, to the tablet,pattern information indicating a set predetermined pattern when thepattern is switched by the switch circuit, and the tablet includes: aplurality of tablet electrodes disposed in a flat surface manner, asignal position detector configured to obtain a coordinate position ofthe alternating-current signal transmitted from said selected one of theelectrodes on a tablet surface based on distribution of a level of asignal induced in each of the tablet electrodes disposed in the flatsurface manner by the alternating-current signal transmitted from theposition indicator, a pattern information receiver configured to receivethe pattern information transmitted from the position indicator, and atilt angle calculator configured to calculate a tilt angle of theposition indicator relative to the tablet surface based on at leastthree coordinate positions and at least three signal intensitiesobtained corresponding to at least three kinds of predeterminedelectrode-selection patterns indicated in the pattern informationreceived by the pattern information receiver.
 5. The position detectingdevice according to claim 4, wherein the switch circuit of the positionindicator sequentially selects one of the at least three electrodes. 6.A position indicator used for inputting an indicated position on atablet based on capacitive coupling with the tablet, the positionindicator comprising: a signal generator configured to generate analternating-current signal; a plurality of electrodes that are disposedat a position indicating part and configured to transmit thealternating-current signal to the tablet; a switch circuit configured tosupply the alternating-current signal to selected one(s) of theplurality of electrodes based on a predetermined electrode-selectionpattern; and a pattern information configured to transmit, to thetablet, pattern information indicating a set predetermined pattern whenthe pattern is switched by the switch circuit.
 7. The position indicatoraccording to claim 6, wherein a first electrode and a second electrodeare disposed at the position indicating part as the plurality ofelectrodes, the switch circuit alternately selects the first and secondelectrodes and supplies the alternating-current signal to the selectedone of the electrodes, and the pattern information transmitter transmitsfirst pattern information to the tablet when the first electrode isselected by the switch circuit, and transmits second pattern informationto the tablet when the second electrode is selected by the switchcircuit.
 8. The position indicator according to claim 6, wherein a firstelectrode and a second electrode are disposed at the position indicatingpart as the plurality of electrodes, the switch circuit always suppliesthe alternating-current signal to the first electrode and switchessupply of the alternating-current signal to the second electrode betweenan on (supply)- and off (no supply)-state, and the pattern informationtransmitter transmits first pattern information to the tablet when thesupply of the alternating-current signal to the second electrode is setto the on-state by the switch circuit, and transmits second patterninformation to the tablet when the supply of the alternating-currentsignal to the second electrode is set to the off-state by the switchcircuit.
 9. A position indicator that has a pen shape and is used forinputting an indicated position on a tablet based on capacitive couplingwith the tablet, the position indicator comprising: a plurality ofelectrodes provided at a position indicating part of the positionindicator, and are arranged on a surface perpendicular to a pen axisdirection.
 10. The position indicator according to claim 9, wherein theposition indicating part has a core body capable of axially moving inresponse to an axial load and the plurality of electrodes are formedintegrally with the core body.
 11. The position indicator according toclaim 9, wherein the position indicating part has a chassis to enclose acore body, and the plurality of electrodes are provided at a tip part ofthe chassis.
 12. The position indicator according to claim 9, whereinthe position indicating part has a core body and two electrodes areprovided on opposing sides of the core body to oppose each other. 13.The position indicator according to claim 9, wherein the positionindicating part has a core body and three electrodes are providedequiangularly around the core body.
 14. The position indicator accordingto claim 9, wherein the position indicating part is a pen tip part ofthe position indicator.
 15. The position indicator according to claim 9,further comprising a switch circuit configured to supply an alternatingcurrent signal to selected one(s) of the plurality of electrodes basedon a predetermined electrode-selection pattern.